A background art device and method for controlling a piston position in a linear compressor will be explained with reference to the attached drawings. FIG. 1 illustrates one example of the background art device for controlling a piston position in a linear compressor, and FIG. 2 illustrates waveforms of high, regular, and low voltages from the AC-DC voltage transformer in FIG. 1, and FIG. 3 explains a definition of top clearance.
Referring to FIG. 1, one example of the background art device for controlling a piston position in a linear compressor is provided with a power source 1 for supplying AC 220V, a triac 2 for switching AC 220 volt from the power source 1 in response to a control signal, a motor 3 operative by AC220V switched thereto through the triac 2 for reciprocating a piston, a stroke generator 4 for generating an AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocating position, a rectifying circuit 5 for rectifying the AC voltage waveform generated at the stroke generator 4, a filter circuit 6 for filtering the voltage waveform rectified at the rectifying circuit 5 into a DC voltage waveform, an AC-to-DC voltage transformer 7 for transforming the DC voltage waveform filtered at the filtering circuit 6 into a corresponding DC voltage, a zero cross detecting circuit 8 for detecting a zero crossing of AC 220V supplied from the power source 1, a microcomputer 9 for converting the DC voltage from the AC-to-DC voltage transformer 7 into a length of piston reciprocation corresponding to the DC voltage, comparing the length of the piston reciprocation to a preset value, and providing a control signal according to a result of the comparison, and a phase controlling part 10 for controlling a firing angle to control a stroke in response to a control signal from the microcomputer 9.
The operation of the background art device for controlling a piston position in a linear compressor of the present invention will be explained.
When the phase controlling part 10 provides a triggering signal for a firing angle at an initial drive of the linear compressor, the triac 2 switches AC220V from the power source 1 to the motor 3, so that the motor 3 reciprocates the piston in a cylinder. In this instance, the stroke generator 4 generates an AC voltage waveform having a fixed frequency: and varied amplitude according to a piston reciprocation position. And, the rectifier circuit 5 rectifies the AC voltage waveform generated at the stroke generator 4, and the filter circuit 6 filters the voltage waveform rectified at the rectifying circuit 5 into a DC voltage waveform. Then, the AC-to-DC voltage transformer 7 transforms the DC voltage waveform filtered at the filtering circuit 6 into a DC voltage corresponding to the DC voltage waveform. And, the zero crossing detection circuit 8 detects a zero crossing of the AC220V from the power source 1, and provides a signal of a zero crossing detection result. According to this, the microcomputer 9 converts the DC voltage from the AC-to-DC voltage transformer 7 into a length of piston reciprocation, compares to a preset value, and provides a control signal according to a result of the comparison. That is, the microcomputer 9 converts the DC voltage from the AC-to-DC voltage transformer 7 into a length of piston reciprocation corresponding to the DC voltage, compares to a preset length for a regular stroke voltage under a regular pressure, and, as shown in FIG. 2, as a result of the comparison, if the DC voltage from the AC-to-DC voltage transformer 7 is a stroke voltage at a high pressure or a low pressure, provides a control signal for altering the stroke voltage into a stroke voltage at a regular pressure. Then, the phase controller 10 provides a signal for controlling a firing angle to control the stroke in response to the control signal from the microcomputer 9. That is, the phase controller 10 provides a control signal for reducing a firing angle according to a control signal for altering a high pressure stroke voltage from the microcomputer 9 into a regular pressure stroke voltage, or a control signal for increasing a firing angle according to a control signal for altering a low pressure stroke voltage from the microcomputer 9 into a regular pressure stroke voltage. According to this, the triac 2, triggered by the control signal from the phase controller 10, controls a voltage phase of the AC220V from the power source 1, and the motor 3 reciprocates the piston in the cylinder according to a phase controlled at the triac 2. That is, the triac 2 controls the voltage phase of the AC220V from the power source 1 according to a control signal for reducing the firing angle from the phase controller 10, to reduce a current to the motor 3, such that the motor 3 in turn reduces the piston reciprocation length in the cylinder shorter, or the triac 2 controls the voltage phase of the AC220V from the power source 1 according to a control signal for increasing the firing angle from the phase controller 10, to increase a current to the motor 3, such that the motor 3 in turn increases the piston reciprocation length in the cylinder shorter. Thus, by repeating the foregoing process, the microcomputer 9 converts the DC voltage from the AC-to-DC voltage transformer caused by the piston reciprocation in the cylinder into a piston stroke length corresponding to the DC voltage, for controlling a piston position.
However, the background art device and method for controlling a piston position in a linear compressor has the following problems.
First, the system is complicated as it involves the rectifying circuit, the filtering circuit, and the AC-to-DC voltage transformer. In addition, there is a difference between actual position and feedback position because of much error at a stroke-feedback device. This error is related to an error at the circuits inclusive of the errors at the motor and the mechanical components. No matter how precisely the system is fabricated, occurrence of collision between the piston and the valves, efficiency deterioration, and increased noise caused by error are not avoidable.
Second, the system has a poor load estimation capability such that, as shown in FIG. 3, load variation at a top clearance portion can not be estimated. That makes it very difficult to control the system, and to predict any environmental variation (e.g., temperature variation) and non-regular characteristics in a set state (e.g., gas leakage, cycle blocking).